Comparison of clasp retention on enamel and composite resin-recontoured abutments following repeated removal in vitro

Statement of problem

Loss of prosthetic retention over time is a concern with removable prostheses. Use of composite resin to modify an abutment contour receiving a removable partial denture clasp may offer a reasonable, less invasive method of improving removable prosthesis retention.

Purpose

The purpose of this study was to evaluate the removal force of clasps over composite resin-recontoured abutments during a simulated 4 years of service.

Material and methods

Twenty first mandibular premolars were selected to form 2 groups of specimens (n=5) resembling a tooth-supported edentulous space. A packable composite resin (Filtek P60) was used to create a 0.25-mm undercut on the buccal abutment surfaces of the composite resin group. Teeth in the natural abutment group were mounted in angulation to produce 0.25-mm undercuts on the buccal surfaces. The chrome-cobalt framework consisted of 2 individually fabricated T-clasps. Both groups were subjected to 4500 cycles of repeated removal using a small shaker. Removal forces were recorded before the repeated removal test (T₀), after 500 and 1000 cycles, and at 1000-cycle intervals thereafter. The mean values of forces between the 2 groups were compared at each stage using the Mann-Whitney test (α=.05).

Results

No debonding occurred during the test. At T₀, the highest and lowest force values were observed in the composite resin group (3.75 N and 17.5 N, respectively). There was a significant difference between the removal forces of the 2 groups after 500 cycles and at test completion (P=.008). Retention loss was 3 times greater in the composite resin group than in the natural abutments group (53.65% vs. 15.80%).

Conclusions

Within the limitations of the study, removal forces of the composite resin-recontoured abutments were threefold less than those of natural abutments after 4 years of simulated service. (J Prosthet Dent 2010;103:240-244)